1. Field of the Invention
The present invention relates generally to surgically implanted materials fabricated from demineralized bone particles, and, more particularly, to such materials which are made up of a coherent shaped mass of elongate bone particles having an improved capacity to maintain its cohesive properties and exhibiting minimal bone particle disassociation upon rehydration.
2. Description of Related Art
The use of demineralized bone powder in the repair of bone defects has been a subject of investigation for some time. Bone powder contains one or more substances, possibly bone morphogenic protein (BMP), which induce bone regeneration at the defect site. See, e.g., Covey et al., xe2x80x9cClinical Induction of Bone Repair with Demineralized Bone Matrix or a Bone Morphogenetic Proteinxe2x80x9d, Orthopaedic Review, Vol. XVII, No. 8, pp. 857-863 (August 1989). According to Habal et al., xe2x80x9cAutologous Corticocancellous Bone Paste for Long Bone Discontinuity Defects: An Experimental Approachxe2x80x9d, Annals of Plastic Surgery, Vol. 15, No. 2, pp. 138-142 (August 1985), autogenous bone which has been granulated into a pastelike material and combined with autogenous blood has been used in the repair of long bone defects in dogs.
U.S. Pat. No. 5,073,373 discloses a deformable, shape-sustaining osteogenic composition, suitable as a filler for osseous defects, in which particles of demineralized bone are uniformly distributed within a carrier which is a liquid polyhydroxy compound such as glycerol. The vast majority of the demineralized bone particles possess random, irregular geometries with an average median length to median thickness ratio of from about 1:1 to about 3:1.
Commonly assigned U.S. Pat. No. 5,314,476 discloses a flowable osteogenic composition containing entangled demineralized bone particles of relatively high median length to median thickness ratio. The flowable osteogenic composition can possess a paste-like or putty-like consistency as well as a liquid or runny consistency.
Commonly assigned U.S. Pat. No. 5,507,813 to Dowd et al., the contents of which are incorporated herein by reference, discloses a surgically implantable shaped material fabricated from elongate bone particles. The shaped material, e.g., in the form of a sheet, is formed by applying a liquid slurry of elongate bone particles, e.g., filaments or fibers, to a porous support, draining excess liquid from the bone particles, optionally while applying a compressive force to the particles during and/or after drainage of the excess liquid, to provide a coherent, shaped wetted mass of bone particles and, optionally, drying the wetted mass. The material thus formed is relatively rigid when dry and, upon contact with a biocompatible liquid, e.g., water, saline solution, etc., becomes pliable and flexible.
Although the shaped bone implant disclosed in the Dowd et al. ""813 patent has proven to be quite effective in the repair of bone defects, the present invention is directed to further improvements in the process of fabricating such implants.
Generally, the coherent shaped mass of demineralized bone particles produced in accordance with the principles of the present invention exhibit an enhanced capacity to retain its cohesive properties and experience minimal bone particle disassociation upon rehydration, thereby improving product handling and application at the operative site.
In a preferred embodiment, a process for fabricating shaped material from bone particles includes the steps of applying a liquid slurry of bone particles to a support, removing excess liquid from the bone particles to provide a coherent shaped mass of bone particles, and warming the shaped-mass of bone particles at a predetermined temperature and for a predetermined time period. Preferably, the bone particles are demineralized. The process may further include the step of drying, e.g., through lyophilization, the shaped-mass of demineralized bone particles subsequent to the step of warming. Preferably, a sheet of demineralized bone particles is produced.